The present invention is directed to ultrasonic sensing and is particularly directed to a sensor system and method in which an analog output of an ultrasonic transducer is processed to provide data to a controller.
Ultrasonic sensors are used to make remote distance measurements. One particular use of ultrasonic sensors is within a vehicle occupant protection system within a vehicle.
One type of protection system includes an actuatable occupant protection device. Examples of actuatable occupant protection devices include inflatable air bags and seat belt system pretensioners. The actuatable devices are actuated in response to one or more conditions for which it is predetermined that the occupant is to be protected. For example, the protection system includes a crash sensor that senses a vehicle collision. A controller of the protection system causes actuation of the protection device in response to a signal indicative of a vehicle collision from the crash sensor.
It is known in the art to adjust or tailor the actuation or deployment of a protection device. For example, the art has recognized that it is not always desirable to inflate an air bag with 100 percent of the available gas provided from a source of inflation fluid. It is known to adjust or tailor the protection deployment based upon one or more sensed occupant characteristics. An occupant protection device that has an adjustable aspect that is adjusted in response to a determination based upon a sensed occupant characteristic is commonly referred to as a xe2x80x9csmartxe2x80x9d device. It is known to use one or more ultrasonic sensors to sense one or more occupant characteristics (e.g., occupant position) for use in determining adjustment of a protection device.
Ultrasonic sensors typically have a piezoelectric ceramic transducer that converts an excitation electrical signal into ultrasonic energy bursts (i.e., a xe2x80x9cpingxe2x80x9d). The energy bursts travel from the ultrasonic sensor, bounce off objects, and are returned toward the sensor as echoes. The transducer converts received echoes into analog electrical signals that are output from the transducer.
In one known ultrasonic sensor system, an analog electrical signal, which is indicative of the received echo signal output from the transducer, is provided to an analog-to-digital (xe2x80x9cA/Dxe2x80x9d) input port of a controller of the system. The controller is programmed to initiate interrupts at regular intervals. During each interrupt, A/D readings are taken, and the digital information is stored in a random access memory (xe2x80x9cRAMxe2x80x9d) within the controller. Specifically, the amplitude of the analog signal is digitally sampled. The controller, processes the digital information stored within the RAM, via at least one algorithm, and makes determinations about the time of flight of the ultrasonic energy burst emitted from the transducer and reflected from an object (e.g., a vehicle occupant) back to the transducer. The time of flight is indicative of the distance between the transducer and the object.
In the known sensor system, the algorithm that the controller performs utilizes a relatively large amount of digital information regarding the transducer output. Thus, the amount of stored digital information is relatively large. Accordingly, a relatively large amount of RAM is necessary to store the information. Also, the digital processing required in the controller""s interrupt, sampling, A/D conversation and storing requires a certain degree of xe2x80x9coverheadxe2x80x9d of the control process.
The present invention provides an ultrasonic sensor system. Transducer means emits an ultrasonic signal in response to an electrical excitation signal and outputs an electrical response signal in response to receipt of a reflected ultrasonic signal received from an object. The electrical response signal has an amplitude indicative of the strength of the reflected ultrasonic signal. Receiver means processes the electrical response signal from the transducer means and outputs an analog, non-oscillating signal. The analog signal has an amplitude indicative of the amplitude of the electrical response signal. Comparator means compares the amplitude of the analog signal to a predetermined amplitude value and outputs a digital signal having a first digital value when the amplitude of the analog signal is less than the predetermined amplitude value, and having a second digital value when the amplitude of the analog signal is greater than the predetermined amplitude value. Controller means processes the digital signal to determine distance between the transducer means and the object.
The present invention also provides the additional aspect of the controller means processing the analog signal output from the receiver means. The analog signal is processed to determine amplitude of the analog signal.
The present invention also provides a method of ultrasonic sensing. An ultrasonic signal is emitted in response to an electrical excitation signal. An oscillating electrical response signal is output in response to receipt of an ultrasonic signal reflected from an object. The electrical response signal has an amplitude indicative of the strength of the reflected ultrasonic signal. The electrical response signal is processed to provide an analog, non-oscillating signal. The analog signal has an amplitude indicative of the amplitude of the electrical response signal. The amplitude of the analog signal is compared to a predetermined amplitude value. A digital signal is provided that has a first digital value when the amplitude of the analog signal is less than the predetermined amplitude value and that has a second digital value when the amplitude of the analog signal is greater than the predetermined amplitude value. The digital signal is processed to determine distance between said transducer mean s and the object.
The present invention also provides the additional aspect of processing the analog signal output from the receiver means. Processing the analog signal results in a determination of amplitude of the analog signal.